The invention relates to an infinitely variable traction roller transmission having traction rollers pivotally supported between toric discs which are mounted opposite each other on input and output shafts. The traction rollers are so arranged that transmission of a torque forces them toward the axis of the toric discs for engagement with the discs.
In the design of toroidal infinitely variable traction roller transmissions, it is a major problem to provide for adequate but not excessive contact forces at any transmission ratio and under any circumstances such as rapid load changes or shock loadings from the input or output end of the transmission.
In many transmissions the contact forces are obtained by forcing the toric discs toward each other with a force which depends on the torque transmitted through the transmission. With this arrangement however it is difficult to provide adequate contact forces as the orientation of the traction roller with regard to the contact force direction is changing with any change in the transmission ratio.
It was already early realized that it would be advantageous to provide the contact forces by loading the traction rollers themselves such that the contact force direction is changing with any transmission ratio change so as to provide for proper traction roller contact forces in any pivotal position thereof.
U.S. Pat. No. 3,087,348 for example discloses a hydraulic piston arrangement disposed in the traction roller pivotal support to force the traction rollers into engagement with the toroidal discs. However such an arrangement requires high hydraulic pressures. It was also found that the reaction time was too long to prevent damage during shock loadings of the transmission. Another embodiment shows a roller-ramp structure, which arrangement however proved to be quite fragile. Both arrangements were relatively space-consuming such that rollers and thrust bearings could not be designed for adequate strength with the limited spaces usually available for the transmissions. U.S. Pat. No. 4,275,610 also employs a hydraulically operated loading arrangement for the traction roller in which the space problem is solved as the hydraulic loading structure is outside the traction rollers. This arrangement however is expensive and, while feasible for normal load applications, it is reacting only relatively slowly such that sudden load changes or shock loading may cause damages to the traction surfaces of the traction rollers and toroidal discs.